Explosive devices are being used increasingly in asymmetric warfare to cause damage and destruction to equipment and loss of life. The majority of the damage caused by explosive devices results from shrapnel and shockwaves. Shrapnel is material, such as metal fragments, that is propelled rapidly away from the blast zone and may damage stationary structures, vehicles, or other targets. Damage from shrapnel may be prevented by, for example, physical barriers. Shockwaves are traveling discontinuities in pressure, temperature, density, and other physical qualities through a medium, such as the ambient atmosphere. Shockwave damage is more difficult to prevent because shockwaves can traverse an intermediate medium, including physical barriers.
Damage from shockwaves may be lessened or prevented by interposing an attenuating material between the shockwave source and the object to be protected. This attenuating material typically may be designed or selected to absorb the energy from the shockwave by utilizing a porous material that distorts as the energy of the shockwave that is absorbed.
U.S. Pat. No. 5,394,786 to Gettle et al. describes a shockwave attenuation device that utilizes an absorbing medium. That assembly includes porus screens that form an enclosure filled with a pressure wave attenuating medium. This attenuating medium may be an aqueous foam, gas emulsion, gel, or granular or other solid particles. However, as shown and described in the drawings of that patent, the shockwave attenuating assembly must be positioned before the explosion occurs and surround the area to be protected. For example, the assembly may be positioned on the side of a vehicle to prevent damage to the vehicle or passengers within.
A similar shockwave attenuation device is described in U.S. Patent Publication No. 2007-0006723 to Waddell, Jr. et al. That device includes a number of cells filled with an attenuating material, such as aqueous foams. However, like the device described in Gettle et al., the pressure-attenuating material and device must be positioned on a structure, surface, or person desired to be protected by the system before the explosion occurs.
One feature common among prior art shockwave attenuation systems is that they require an intermediate medium or structure that acts to attenuate the force of the shockwave by absorbing the energy of the shockwave. Although only a portion of the shockwave may pass through the medium, the energy of the shockwave is nevertheless significantly reduced by the intermediate medium. However, because these systems are structural, they must be fixed in place before a shockwave is created. Further, these shockwave attenuation systems may not protect an entire vehicle or person. For example, attenuating panels are not transparent and therefore cannot be placed over windows or used as facemasks in helmets. They also may be bulky and heavy, and therefore negatively impact the performance of a vehicle on which they are mounted.
Such prior art shockwave attenuation systems may not be effective to protect waterborne assets in which an incoming threat may be in the form of a torpedo, ballistic shell, bomb or a naval mine. Therefore, a need exists for a shockwave attenuation device that is capable of dynamically interposing a medium between an explosion source and a protected asset. There is also a need for an intermediate medium that effectively attenuates the energy from a shockwave and that allows for protection of a protected asset in a marine environment.